When a surgeon operates on the legs or arms, nerve block anesthesia may be performed to numb or anesthetize the nerves innervating the region being operated upon. Performance of nerve blocks consists of several phases. In the first phase, the operator inserts the needle in the presumed vicinity of the nerve(s) to be blocked. In doing so, the operator may insert the needle “blindly” relying on anatomical landmarks, the operator may try to elicit “paresthesia,” whereby the nerve is touched by the needle and the patient perceives “a shock” traveling down the nerve being touched, or the operator may use a nerve stimulator to elicit the motor response (twitch) of the nerve being sought. Whichever method is used, the operator hopes to be in the immediate vicinity to the nerve (which is necessary for reliable nerve blocks) and not in the nerve itself (which may result in traumatic nerve injury when the local anesthetic is injected into the nerve). It is important to emphasize that all three methods used to locate nerves at best approximate the needle position in relationship to the nerve and not confirm it with absolute accuracy. Consequently, with these three described methods for localizing nerves during nerve blocks, the needle tip may inadvertently be inserted into the nerve itself. The resultant injection directly into the nerve(s) may result in significant nerve injury.
Regional anesthesia is widely thought to have a number of advantages over general anesthesia. Regional anesthesia is an effective, low-cost technique that provides a means of selectively anesthetizing a region of the body while minimally interfering with the patient's vital systems. However, one of the major disadvantages of regional anesthesia and nerve blocks in particular is the possibility of nerve damage during administration of nerve blocks or regional anesthesia. Other drawbacks include the risks of systemic and local toxic complications. The primary target for local anesthetic effect in regional anesthesia is neural tissue, such as peripheral nerves, nerve roots, and spinal cord. Thus, it may not be surprising that the most common and troublesome local complications of nerve blocks and regional anesthesia involve the peripheral nerves. Such complications are, fortunately, rare, but they can cause considerable problems for both patient and physician. Of note, even the most careful anesthesiologist will occasionally encounter a PNS complication. For instance, in a survey of hand surgeons regarding experience of neurologic complications associated with axillary block anesthesia, 171 (21%) of the responding 800 surgeons had seen a total of 249 major complications (i.e., lasting at least a year), and 521 (65%) had dealt with minor neurologic sequelae (Stark, “Neurologic Injury from Axillary Block Anesthesia,” J. Hand Surg. 21A, 391 (1996)). Thus, about one of five hand surgeons has seen a major neurologic sequela that might have been related to a nerve block. While the overall incidence of nerve damage after nerve blocks is relatively low, the consequences can be catastrophic and result in a temporary or permanent injury to the nerve, loss of limb function and paralysis. See, e.g., Auroy et al., “Serious Complications Related to Regional Anesthesia: Results of a Prospective Survey in France,” Anesthesiology, 87, 479-484 (1997); Eisenach, “Regional Anesthesia: Vintage Bordeaux (And Napa Valley),” Anesthesiology, 87, 467-9 (1997). Indeed, the neurologic complications after regional anesthesia are among the most commonly discussed issues at various anesthesia conferences, and a common topic of many scientific publications. Lesions to the brachial plexus seem to be reported most frequently. See, e.g., Bonica et al., “Brachial Plexus Block Anesthesia,” Am. J. Surg., 78, 65 (1949); Moberg et al., “Brachial Plexus Block Analgesia with Xylocaine,” J. Bone Joint Surg., 33A, 884 (1951); Wolley et al., “Neurological sequelae of brachial plexus nerve block,” Ann. Surg., 149, 53 (1959); Brand et al., “A Comparison of Supraclavicular and Axillary Techniques for Brachial Plexus Blocks,” Anesthesiology, 22, 226 (1961); Schmidt et al., “Komplikationen und Gefahren der Plexus-brachialis-Anesthesie unter besonderer Berucksictinung von Langzeitschaden,” Anasth. Intensivther. Notfallmed., 16, 346 (1981); de Jong, “Axillary block of the brachial plexus,” Anesthesiology, 22, 215 (1961); Hamelberg et al., “Perivascular Axillary Versus Supraclavicular Brachial Plexus Block and General Anesthesia,” Anesth. Analg., 41, 85 (1962); Wall, “Axillary nerve blocks,” Ann. Surg., 149, 53 (1959); Moore et al., “Bupivacaine: a Review of 11,080 Cases,” Anesth. Analg., 57, 42 (1978); Selander et al., “Parasthesiae or No Parasthesiae? Nerve Lesions after Axillary Blocks,” Acta. Anaesth. Scand., 23, 27 (1979); Plevak et al., “Paresthesia Vs. Non Paresthesia—the Axillary Block,” Anesthesiology, 59, A216 (1983); Winchell et al., “The incidence of neuropathy following upper extremity nerve blocks,” Reg. Anesth., 10, 12 (1985); Tourtier et al., “Complications of Axillary Block Using Two Techniques: Experience with 1400 Cases,” Anesthesiology, 71, A726 (1989); Davis et al., “Brachial Plexus Anesthesia for Outpatient Surgical Procedures on an Upper Extremity,” Mayo Clin. Proc., 66, 470 (1991); Stan et al., “The Incidence of Neurovascular Complications Following Axillary Brachial Plexus Block Using a Transarterial Approach,” Reg. Anesth., 20, 486 (1995); Lofstrom et al., “Late Disturbances in Nerve Function after Block with Local Anesthetic Agents.” Acta. Anesth. Scand., 10, 111 (1966); Mogensen et al., “Posttraumatic Instability of the Metacarpophalangeal Joint of the Thumb,” Hand, 12, 85 (1980).
One of the mechanisms of nerve injury is inadvertent insertion of the needle into a nerve with consequent injection of local anesthetic inside the nerve. This in turn may result in either mechanical trauma to the nerve, ischemic injury to the nerve due the resultant increase in endoneural pressure due to the high pressures inside the nerve, and/or endoneral edema. Indeed, experimentally, it was found that intrafascicular injections in rabbit sciatic nerve in vivo can produce endoneural pressures of more than 700 mm Hg, and after such injections the endoneural pressure could exceed the estimated capillary perfusion pressure for about 15 minutes. During this period, the nerve fascicle is both ischemic and vulnerable to otherwise toxicologically neutral local anesthetic solutions. Selander et al., “Longitudal Spread of Intraneurally Injected Local Anesthetics,” Acta Anesth. Scand., 22, 622 (1978). Similar conditions can also occur in humans, and admixture of epinephrine with local anesthetic can enhance ischemia when injected intraneuronally and thus increase the risk of nerve injury. Selander et al., “Parasthesiae or No Parasthesiae? Nerve Lesions after Axillary Blocks,” Acta Anaesth. Scand., 23, 27 (1979). The pressures on normal injection of local anesthetics in humans range from about 500 mm Hg to about 1200 mm Hg. Higher pressures may indicate an intraneuronal injection. Hadzic et al., “Injection Pressure During Peripheral Nerve Blockade,” Anesthesiology, Abstract (2002).
The current recommendations to decrease the risk of intra-neuronal injections consist of slow injection to avoid high injection pressures and the avoidance of injection when high pressures are noticed during injection of local anesthetic. Finucane, Complications of Regional Anesthesia, Churchill Livingstone, N.Y. (1999). However, these recommendations assume that the operator or operators are able to perceive the difference between “normal” and “abnormal” injection pressures and take appropriate actions when “abnormal” injection pressures are observed. However, these judgments are prone to subjective interpretation and/or the “feel” of the operators and not on any objective measurements (e.g., measured injection pressure, speed, or similar variables). The ability of different operators to estimate and/or control the injection (especially as with regard to pressure) is further complicated by differences in hand strength and experience among operators as well as differences in resistance to injection for various needle types, lengths, and lumen calibers. In addition, in clinical practice, it is common practice for an operator (e.g., anesthesiologist, nurse anesthesiologist, other anesthesia providers, and the like) to perform the needle placement with an assistant (often without significant experience in nerve blockade) who injects the local anesthetic. This practice poses a risk of exerting too high pressures during injection and possible unrecognized intraneuronal injection. In addition, the operator typically uses both hands to perform the procedure (i.e., place the injection needle in the appropriate location relative to the nerve) and cannot easily determine and/or control the amount of force and pressure that the assistant may employ to inject the local anesthetic.
Moreover, forceful and/or fast injections of local anesthetic solutions can lead to a higher risk of systemic local anesthetic toxicity (e.g., seizures, arrhythmia, cardiovascular collapse, and death) due to tracking of local anesthetic between tissue layers and inadvertent intravascular injections. Additionally, intraneuronal and rapid injections of local anesthetics can backtrack to the spinal column and result in unintended epidural or spinal anesthesia with potentially disastrous consequences (Selander et al., “Longitudal Spread of Intraneurally Injected Local Anesthetics,” Acta Anesth. Scand., 22, 622 (1978); Tetzlaff et al., “Subdural Anesthesia as a Complication of an Interscalene Brachial Plexus Block,” Regional Anesthesia, 19, 357-359 (1994); Dutton et al., “Total Spinal Anesthesia after Interscalene Blockade of the Brachial Plexus,” Anesthesiology, 80, 939-941 (1994)).
Various attempts have been made to improve anesthesia instruments. See, e.g., U.S. Pat. No. 5,119,832 (Jun. 9, 1992); U.S. Pat. No. 5,378,241 (Jan. 3, 1995); U.S. Pat. No. 4,994,036 (Feb. 19, 1991); U.S. Pat. No. 4,775,367 (Oct. 4, 1988); U.S. Pat. No. 4,889,529 (Dec. 26, 1989); U.S. Pat. No. 4,917,670 (Apr. 17, 1990); U.S. Pat. No. 4,917,668 (Apr. 17, 1990); U.S. Pat. No. 5,085,631 (Feb. 4, 1992); U.S. Pat. No. 5,106,376 (Apr. 21, 1992); U.S. Pat. No. 5,135,525 (Aug. 4, 1992); U.S. Pat. No. 5,312,374 (May 17, 1994); U.S. Pat. No. 5,328,479 (Jul. 12, 1994); U.S. Pat. No. 5,512,052 (Apr. 30, 1996); U.S. Pat. No. 5,630,802 (May 20, 1997). None of these attempts, however, focused on controlling and/or measuring the pressure and/or injection speed during injection to avoid an inadvertent intraneuronal injection, or rapid spread, and/or absorption of local anesthetics during nerve blockade/regional anesthesia.
Thus, it is clear that a more objective and reproducible method of monitoring and/or controlling the pressure and/or injection speed during nerve blockage injection, especially by less experienced personnel and/or assistants, would be beneficial in order to decrease the possibility of intraneuronal injection. The present invention provides such a method and apparatus.